1. Field of the Invention
The present invention relates generally to guided artillery shells and more specifically, to spinning projectiles which utilize rate gyro instrumentation to provide electrical signals indicative of the time rate of change of attitude of such projectiles. A principal feature of the present invention is the use of such a rate gyro in a spinning projectile wherein the gyroscope rotor derives its spin from the projectile body and wherein a flexible joint serves as a gimbal bearing whereby to eliminate a spin motor with its associated bearings and also to eliminate gimbal bearings.
2. Prior Art
The use of rate gyros as instruments for providing an inertial reference in the navigation systems of aircraft and missiles is well-known. The need for a rate gyro instrument to provide a stable reference for a moving vehicle arises because of the high maneuverability and speed of aircraft and missiles and the lack of outside reference points. Rate gyros are attitude rate transducers which provide an output proportional to the anglar velocity or time rate of change of attitude of the vehicle. Typically, pick off points are provided in the gyroscope and provide an output which is representative of gimbal deflection about an output axis in response to attitude rate changes about an input axis. Gyro attitude transducers are usually designed as two degree of freedom gyros providing an output for each of two of a vehicle's three attitude planes. Such gyros provide an inner gimbal for one axis and an outer gimbal for the other axis with a separate pick off for each axis.
A variety of different torque producing devices may be used to spin a rotor to generate the basic gyroscopic action. Most typical, are ac or dc motors which are used to turn the rotor. Some gyros use a clock spring wound before each use or a pyrotechnic charge which when activated forces a stream of combustion gases into a small turbine.
With the growing sophistication of artillery shells which in fact provide the capability for some form of trajectory control, it has become advantageous to use such gyroscopes in artillery shells as well. Unfortunately, there are two substantial problems associated with using relatively sophisticated inertial reference gyro instrumentation in artillery shells. One such problem is that the gyro instrument can become a significant cost factor in the overall cost of a shell and because the artillery shell is clearly an expendable, the high manufacturing costs of an inertial reference instrument for an expendable projectile can be a significant disadvantage.
A second significant problem stems from the fact that a conventional gyroscope instrument utilizes a variety of bearings, bearings associated with the spin motor and bearings associated with the gimbals. Unfortunately, bearings do not normally survive well under the conditions of intense acceleration such as those which are incurred by a projectile in the gun tube. Gun fired projectiles may in fact be subject to acceleration exceeding 60,000 times the force of gravity. Thus, there is an inherent conflict between the conventional use of bearings in gyro instrumentation and the sensitivity of such bearings to forces of acceleration, particularly intense forces incurred in gun fired projectiles. In the past this conflict has been resolved by either significantly limiting the acceleration to which the projectile can be subjected, by limiting the operational mode of the gyroscope to protect the bearings during the initial firing of the projectile or perhaps more significantly, by utilizing bearings which are specially manufactured to withstand high acceleration stresses, which of course results in a more substantial cost of the instrument.
The present invention overcomes the aforementioned problems by eliminating all bearings in a rate gyro instrument used for inertial reference purposes in a gun fired projectile. This is accomplished by eliminating the spin motor and therefore, the associated bearings and by substituting a flexible joint for the gimbal thereby eliminating gimbal bearings.
The applicant knows of no prior art which combines the features of the present invention to entirely eliminate bearings thereby making it possible to utilize an inertial reference gyro in a gun fired projectile where operation of the gyro may be permitted during firing despite intense acceleration. The most relevant patents known to the applicant in this regard include the following U.S. Pat. Nos.:
3,281,094: Jasperson PA1 3,585,866: Ensinger PA1 4,116,404: Howell PA1 4,189,948: Buckley et al. PA1 4,286,370: Craig PA1 4,291,849: Rodgers et al. PA1 4,389,028: Kalivretenos et al. PA1 4,397,185: Craig et al. PA1 4,431,150: Epperson Jr. PA1 Re. 30,290: Craig et al.
U.S. Pat. No. 4,431,150 to Epperson, Jr. is directed to a gyroscopically steerable bullet. The bullet is provided with a mechanism for locking the rotor of a gyroscope to the projectile body with the spin axis of the rotor and the projectile axis in a coincident line. The rotor is then spun when the projectile body is spun about its axis during launching. The bullet is also provided with means for unlocking the rotor after the projectile body and rotor have been spun during the launch phase so that the rotor may then spin freely thereafter. Means are provided to despin the projectile body while transferring angular momentum to the free spinning rotor.
U.S. Pat. No. 4,397,185 to Craig et al discloses an inertial instrument with a cup-shaped inertial mass. The rotor includes a flange which extends over the upper portion of the gimbal suspension. Within the interior of the rotor housing is a magnet and resting on the magnet is a pole piece supporting a second magnet. The pole piece separates the two magnets and is mounted over an upper bucking magnet to channel flux and enclose the magnetic field.
U.S. Pat. No. 4,286,370 to Craig is directed to a universal joint flexure hinge suspension system for a tuned inertial instrument.
U.S. Pat. No. 4,116,404 to Howell provides annular containers to dynamically balance a rocket during flight. The containers are filled with a high density fluid and when spin is induced in the rocket the radial center of gravity shifts to the spin axis and the fluid couples itself to the outside diameters of the rocket.